STEP’s Plan for Understanding REBCO Coated Conductors in the Fusion Environment

The UKAEA’s Spherical Tokamak for Energy Production (STEP) program aims to demonstrate the ability of a low aspect ratio tokamak to generate net electricity from deuterium-tritium fusion. Specifically, its aim is to deliver a prototype fusion power plant, targeting the 2040s, and a path to the commercial viability of fusion, by engaging with and invigorating relevant industries and the supply chain. STEP will utilize REBCO coated conductors (CCs) as the current carrier in the bulk of its magnets. It has been recognized that neutron irradiation leads to the degradation of REBCO’s superconducting properties and that this degradation will limit STEP’s availability. However, current knowledge does not cover all the conditions that REBCO CCs will be subjected to while operating in STEP’s magnets. Recent preliminary works have shown that these additional service conditions could exacerbate the degradation in REBCO’s superconducting properties, and therefore, they each require further investigation. STEP’s Confinement Systems’ Materials group has developed a plan to characterize the superconducting properties of REBCO under conditions as-close-as-reasonably-possible to those within STEP prior to its construction. The campaign will thoroughly test and validate the choice of REBCO CCs used in the construction of STEP magnets. Here, STEP’s current understanding of REBCO and how it is affected by irradiation are presented, followed by the details of experiments designed to develop our knowledge of how REBCO will fare when subjected to fusion neutron irradiation.